Control strategy of mode transition with engine start in a plug-in hybrid electric bus

Torque coordinated control of the relevant power sources has an important impact on the vehicle dynamics and driving performance during the mode transition of the hybrid electric vehicles(HEVs). Considering the dynamic impact problem caused by mode transition, this paper, based upon the structural features of axially paralleled hybrid power system, introduces the bumpless mode switching control theory to analyze multi-mode transition. Firstly, the state transition process is abstracted as the state space transition problem of hybrid system. Secondly the mode transition is divided into four sub-states, and the state model of each sub-state is established. Thirdly, taking the cost functions as the optimization objective, the state switching process is solved, and the control vectors of each switching process are obtained. Simulation and experimental results show that the proposed control strategy can effectively suppress torque fluctuation, avoid longitudinal acceleration impact, and improve driving performance.